[3.11.y.z extended stable] Patch "xen/manage: fix potential deadlock when resuming the console" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    xen/manage: fix potential deadlock when resuming the console

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From c2972883e90f56564832033f214887540af72256 Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel at citrix.com>
Date: Wed, 2 Jul 2014 17:25:23 +0100
Subject: xen/manage: fix potential deadlock when resuming the console

commit 1b6478231c6f5f844185acb32045cf195028cfce upstream.

Calling xen_console_resume() in xen_suspend() causes a warning because
it locks irq_mapping_update_lock (a mutex) and this may sleep.  If a
userspace process is using the evtchn device then this mutex may be
locked at the point of the stop_machine() call and
xen_console_resume() would then deadlock.

Resuming the console after stop_machine() returns avoids this
deadlock.

Signed-off-by: David Vrabel <david.vrabel at citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
[ luis: backported to 3.11: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/xen/manage.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index 624e8dc24532..0bc8086064ca 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -95,7 +95,6 @@ static int xen_suspend(void *data)

 	if (!si->cancelled) {
 		xen_irq_resume();
-		xen_console_resume();
 		xen_timer_resume();
 	}

@@ -152,6 +151,10 @@ static void do_suspend(void)

 	err = stop_machine(xen_suspend, &si, cpumask_of(0));

+	/* Resume console as early as possible. */
+	if (!si.cancelled)
+		xen_console_resume();
+
 	dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);

 	if (err) {
--
1.9.1